This invention relates to a device for electrical stimulation of smooth muscle comprising a portion of the gastro-intestinal tract, a method for using the device of the within invention and a method for electrical stimulation of the smooth muscle.
Many different ways of stimulating gastro-intestinal function have been explored, including pharmacological, neural, purely electrical, and combined methods. In particular, gastric electrical stimulation has been a subject of research investigation for many years:
1. Bellahsene, B. E., C. D. Lind, B. D. Schirmer, O. L. Updike, and R. W. McCallum, xe2x80x9cAcceleration of gastric emptying with electrical stimulation in a canine model of gastroparesisxe2x80x9d Am. J. Physiol. 262(5 Pt 1):G826-34, 1992;
2. Berger, T., J. Kewenter, and N. G. Kock, xe2x80x9cResponse to Gastrointestinal Pacing: Antral, Duodenal and Jejunal Motility in Control and Postoperative Patientsxe2x80x9d Annals of surgery 161:139-44, 1966;
3. Chen, J. D., B. D. Schirmer, and R. W. McCallum xe2x80x9cSerosal and cutaneous recordings of gastric myoelectrical activity in patients with gastroparesisxe2x80x9d Am. J Physiol. 266(1 Pt 1):G90-8, 1994;
4. Daniel, E. E. and S. K. Sarna xe2x80x9cDistribution of Excitory Vagal Fibers in Canine Wall to Control Motilityxe2x80x9d Gastroenterology 71:608-13, 1976;
5. Familoni, B. O., T. L. Abell, G. Voeller, A. Salem, 0. Gaber, and D. Nemoto xe2x80x9cLong-term electrical stimulation of the human stomachxe2x80x9d Gastroenterology 106(2):A496, 1994;
6. Sama, S. K., K. L. Bowes, and E. E. Daniel xe2x80x9cGastric Pacemakersxe2x80x9d Gastroenterology 70:226-31, 1976;
7. Quast, D. C., Beall, A. C., and DeBakey, M. E., xe2x80x9cClinical Evaluation of the Gastrointestinal Pacerxe2x80x9d Surg. Gynec. Obstet. 120:35-40, 1965;
8. Miedama, B. W., Sarr, M. G., and Kelly, K. A. xe2x80x9cPacing the Human Stomachxe2x80x9d Surgery 111:143-50, 1992;
9. Hocking M. P., Vogel, S. B., and Sininsky, C. A. xe2x80x9cHuman gastric myoelectric activity and gastric emptying following gastric surgery and with pacingxe2x80x9d Gastroenterology 103:1811-1816, 1992;
10. Familoni, B. O., Abell, T. L., Nemoto D., Voeller, G., and Johnson, B. xe2x80x9cEfficacy of electrical stimulation at frequencies higher than basal rate in canine stomachxe2x80x9d Digestive Diseases and Sciences 42:892-897, 1997;
11. Christensen, J. xe2x80x9cResponses of the smooth muscle segment of the opossum esophagus to distention and electrical stimulation, and their modification by antagonistxe2x80x9d In: Gastrointestinal Motility, International Symposium on Motility of the Gastrointestinal tract, pp. 167-174, Erlangen, July 15-16, 1969).
It is now well known that gastric contractions are controlled by gastric electrical activity (xe2x80x9cGEAxe2x80x9d) (Sarna et. al., 1976). Moreover, when contractions are present, their temporal and propagation organization is strongly related to the organization of GEA. Therefore, electrical stimulation of the stomach may have particular application to a condition known as gastroparesis, in which the stomach is incapable of grinding, mixing and transmitting the food to the duodenum, and to other conditions in which gastric emptying time is abnormally delayed (Bellahsene et. al., 1992; Chen et. al., 1994).
Recently, gastric electrical pacemaking has once again become a subject of intensive investigation (Eagon J C and Kelly K A xe2x80x9cEffect of electrical stimulation on gastric electrical activity, motility and emptyingxe2x80x9d Neurogastroenterologyand Motility. 7:39-45, 1995; The GEMS Group xe2x80x9cElectrical stimulation for the treatment of gastroparesisxe2x80x94preliminary report of a multicenter international trialxe2x80x9d Gastroenterology, 110:A668, 1996; Chen J D Z, Lin Z Y, Schirmer B D, Williams R D, Ross B and McCallum R W xe2x80x9cEffect of gastric pacing with optimal parameters on gastric emptying in patients with gastroparesisxe2x80x9d In: Proceedings of XV Int. Symposium on Gastrointestinal Motility, p. 42, Rome, Italy, October 1995; McCallum, R. W., Chen, J. D. Z., Lin, Z., Schirmer, B. D., Williams, R. D., and Ross R. A. xe2x80x9cGastric pacing improves emptying and symptoms in patients with gastroparesisxe2x80x9d Gastroenterology 114:456-61, 1998).
In 1963, Bilgutay et. al. (Bilgutay A M, Wingrove R, Griffin W O, Bonnabeau R C and Lillehei C W xe2x80x9cGastro-intestinal Pacing. A New Concept in the Treatment of Ileusxe2x80x9d Ann. Surg., 158;338-43, 1963) described marked shortening of the duration of postoperative ileus in patients using neural electric gastric stimulation (xe2x80x9cNEGSxe2x80x9d) with a single antral intraluminal electrode and a single cutaneous reference electrode. However, subsequent well-controlled studies have failed to confirm any significant effect of single-electrode NEGS on antral contractions or postoperative ileus (Quast et. al., 1965 and Miedama et. al., 1992).
Later studies have focused upon Electrical Control Activity (xe2x80x9cECAxe2x80x9d) entrainment, termed Gastric Electrical Pacing (xe2x80x9cGEPxe2x80x9d) by Sama et. al., 1976. Distal antral stimulation in dogs produced a delay in emptying of liquids and solids. Proximal stimulation to entrain ECA to a higher frequency was found to have no effect on antral emptying. These findings were confirmed by Kelly K A, and Code CF xe2x80x9cDuodenal-gastric reflux and slowed gastric emptying by electrical pacing of the canine duodenal pacesetter potentialxe2x80x9d Gastroenterol., 72:429, 1977. Kelly et. al., 1977 demonstrated retrograde propulsion of duodenal contents with distal duodenal stimulation and entrainment of the duodenal pacesetter potential.
J. C. Eagon et. al., 1995 studied carefully the effects of low-frequency (0-20 Hz) electrical stimulation on canine gastric electrical activity (GEA), motility and emptying and concluded that although an increment of GEA frequency was observed when stimulating at 6 and 30 cycles-per-minute (cpm), gastric contractions and emptying were not affected by stimulation in the low frequency range. More optimistic findings were reported by The GEMS Study Group, 1996 in improvement of nausea and vomiting in humans, but no dramatic change in gastric emptying was evident.
Chen et al., October 1995, described slight acceleration of gastric emptying in a pilot study of a small number of patients with gastroparesis by performing GEP at one site on the greater curvature of the stomach and entraining ECA to a frequency 10% higher than the electrophysiological or basal. Further, Bellahsene et. al., 1992, in a canine model of gastroparesis, showed acceleration of gastric emptying after glucagon-evoked dysrhythmia and GEP in five vagotomized dogs. However, the study failed to show significant improvement in gastric emptying without the artificially created dysrhythmia thus questioning the ability of GEP alone to accelerate gastric emptying.
Familoni et al., 1997 in a more recent investigation using a canine model of GEP described some increased contractile activity when stimulating with frequency 4-5 times higher than the electrophysiological, but they did not measure gastric emptying. In addition, another study (The GEMS Group, 1996) reported diminished nausea and vomiting in patients treated with GEP, but the impact of pacing on gastric emptying remained questionable.
In 1998 McCallum et al., 1998 described acceleration of gastric emptying in patients with gastroparesis by performing GEP at a single site on the greater curvature of the stomach and entraining ECA to a frequency 10% higher than the basal. However, the experimental protocol in this study provided for continuing prokinetic drug therapy during the stimulation, and therefore the effect of GEP alone remained obscured.
The within invention specifically utilizes a mathematical or computer model of gastric stimulation in order to derive the parameters of the electrical stimuli required to produce artificially propagated contractions in the stomach.
Mirrizzi et. al., 1985 (Mirrizzi N., R. Stella, U. Scafoglieri xe2x80x9cA model of extra cellular wave shape of the gastric electrical activityxe2x80x9d Med. Biol. Eng. and Comput, 23:33-37, 1985) and Mirrizzi et. al., 1986 (Mirrizzi N., R. Stella, U. Scafoglieri xe2x80x9cModel to stimulate the gastric electrical control activity on the stomach wall and on abdominal surfacexe2x80x9d Med. Biol. Eng. and Comput, 24:157-163, 1986) suggest a conical dipole model of gastric electrical activity. The gastric electrical field was considered to be a result of electrical dipoles pointing towards the centre of the stomach in an approximately 2 mm. wide ring of depolarized smooth muscle cells. The conical dipole model assumes that the first such ring originates in the mid-corpus. With the continuous repolarization of the proximal layer of cells in the ring and the depolarization of the distal layer, the ring can be thought of as a dynamic entity that moves with an increasing velocity towards the pylorus, thus representing the dynamics of the depolarization-repolarization phenomena that take place in a healthy stomach.
However, a recent study by the inventors of the within invention (Mintchev, M. P. and K. L. Bowes xe2x80x9cConoidal Dipole Model of the Electrical Field Produced by the Human Stomachxe2x80x9d Med. Biol. Eng. and Comput. 33:179-85, 1995) suggested a conoidal dipole model of gastric electric field (the xe2x80x9cconoidal modelxe2x80x9d) as an improvement over the previously known conical dipole model. In the conoidal model, as described in detail in Mintchev et. al., 1995, the area S of a xcex4-wide ring of depolarized cells represented as dipoles pointing toward the center was given with:
S=2xcfx80xcex4r(t)xe2x80x83xe2x80x83Equation [1]
where r(t) represented the radii of the circles that build up this ring of dipoles. On the other hand, the relationship between the vector of the dipole density D and the vector of the equivalent dipole moment P (which is directly related to the number of depolarized cells in the ring and their depolarization level) is given with:
D=P/Sxe2x80x83xe2x80x83Equation [2]
The articles by Mirrizzi et al., 1985 and 1986, set out above, suggested that |P| could be considered constant and estimated its value to be 2.2xc3x9710xe2x88x9216 C.m. They assumed that the charge distribution on each side of a given polarized cell in the ring is approximately equal, and the number of polarized cells in the ring remains the same, while the density of the cells increases in distal direction with the decrement of S. When considering gastric stimulation in the conoidal model, this assumption is deviated from and |P| is considered to be a variable. In fact, it is believed, and the conoidal model assumes, that changes in gastric electrical activity (GEA) associated with contractions cause the amplitude of this vector to fluctuate. However, these fluctuations could very well be obscured when the vector distance p between the point of interest and the infinitesimal area segment dS located on the ring of depolarized cells is sufficiently great (e.g. in electrogastrography):
VQ=[xc2xcxcfx80xcex5]∫(s)[D.xcfx81/|xcfx81|3]dSxe2x80x83xe2x80x83Equation [3]
Although the conoidal model and equation [3] relate to the spontaneous GEA of a normal stomach (as is discussed further below), it is believed that the conoidal model may be able to reconstruct the temporal and propagation organization of the missing contractions in a gastroparetic stomach.
There is therefore a need for a method and a device for the electrical stimulation of smooth muscle comprising a portion of the gastro-intestinal tract in order to facilitate or aid at least a partial emptying of such portion. Further, there is a need for a method and a device for the electrical stimulation of the smooth muscle of the stomach. Finally, there is a need for a method and a device which utilize the conoidal model to derive the parameters of the electrical stimulus required to produce artificially propagated contractions in the stomach sufficient to facilitate at least a partial emptying of the stomach.
This invention relates to a device for electrical stimulation of smooth muscle comprising a portion of the gastro-intestinal tract, a method for using the device of the within invention and a method for electrical stimulation of the smooth muscle. In particular, the device and the methods relate to the electrical stimulation of the smooth muscle in a manner such that local contractions of the portion of the gastro-intestinal tract are artificially propagated therethrough in order to facilitate or aid at least a partial emptying of such portion. Preferably, the local contractions are artificially propagated by phase locking or time shifting the electrical stimulus, which is applied to the smooth muscle circumferentially about the portion at two or more locations. Further, the electrical stimulus applied at each location to produce the desired local contraction is preferably variable such that the characteristics or nature of the electrical stimulus may be varied between locations.
Preferably, when stimulating the smooth muscle of the stomach, the within invention utilizes the conoidal mathematical or computer model of gastric stimulation in order to derive the parameters of the electrical stimuli required to produce artificially propagated contractions in the stomach. Further, the conoidal model is preferably used to calculate the positions or locations for application of the electrical stimuli in the stomach, to determine the configurations of circumferential electrode sets utilized by the device of the within invention to produce the local circumferential contractions of the stomach and to determine the nature or characteristics of the phase-locked electrical stimulus applied at each location or position in order to recreate a distally moving peristalsis.
In the preferred embodiment, the within invention is directed at a method and a device for simulating gastric electrical stimulation using the conoidal model of gastric electrical activity. Thus, the invention may suggest a possible avenue toward reliable gastric pacing. Further, the invention implements the concept of artificially propagated contractions by phase-locking or time-shifting local non-propagated contractions produced by variable electrical stimuli applied at selected locations in the stomach, by circumferential electrode sets of the within invention. As described above, the temporal and propagation organization of gastric electrical activity described in the conoidal model is used to derive the geometry of the stimulating electrode sets and to determine the characteristics, nature and timing of the phase-locked electrical stimuli applied to the different circumferential electrode sets.
In a first aspect of the invention, the invention is directed at a device for electrical stimulation of smooth muscle comprising a portion of the gastro-intestinal tract, wherein the portion of the gastro-intestinal tract defines a longitudinal axis extending therethrough. The device is comprised of:
(a) a proximal electrode set for arrangement circumferentially about the portion of the gastro-intestinal tract in a plane substantially perpendicular to the longitudinal axis such that the smooth muscle may be stimulated thereby to produce a local circumferential contraction of the smooth muscle at the location of the proximal electrode set;
(b) at least one distal electrode set for arrangement circumferentially about the portion of the gastro-intestinal tract in a plane substantially perpendicular to the longitudinal axis and in axially spaced relationship relative to the proximal electrode set such that the smooth muscle may be stimulated thereby to produce a local circumferential contraction of the smooth muscle at the location of the distal electrode set;
(c) at least one power source for providing a variable electrical stimulus to the proximal and distal electrode sets sufficient to stimulate the smooth muscle to produce the local circumferential contractions, wherein the electrical stimulus is variable between each of the proximal and distal electrode sets;
(d) a timing mechanism, associated with the power source, for phase locking the electrical stimulus such that the electrical stimulus is applied to the proximal and distal electrode sets successively and repetitively;
wherein the axially spaced relationship between the electrode sets and the timing of the electrical stimulus applied to the electrode sets are selected such that the local circumferential contractions are artificially propagated distally through the portion of the gastro-intestinal tract.
In a second aspect of the invention, the invention is directed at a method for electrical stimulation of smooth muscle comprising a portion of the gastro-intestinal tract, wherein the portion of the gastro-intestinal tract defines a longitudinal axis extending therethrough and wherein the method is performed using a device comprised of a proximal electrode set and at least one distal electrode set. The method is comprised of the steps of:
(a) arranging the proximal electrode set circumferentially about the portion of the gastro-intestinal tract in a plane substantially perpendicular to the longitudinal axis such that the smooth muscle may be stimulated thereby to produce a local circumferential contraction of the smooth muscle at the location of the proximal electrode set;
(b) arranging each of the distal electrode sets circumferentially about the portion of the gastro-intestinal tract in a plane substantially perpendicular to the longitudinal axis and in axially spaced relationship relative to the proximal electrode set such that the smooth muscle may be stimulated thereby to produce a local circumferential contraction of the smooth muscle at the location of the distal electrode set;
(c) applying a variable electrical stimulus to the proximal and distal electrode sets sufficient to stimulate the smooth muscle to produce the local circumferential contractions, wherein the electrical stimulus is variable between each of the proximal and distal electrode sets and wherein the electrical stimulus is phase-locked such that the electrical stimulus is applied to the proximal and distal electrode sets successively and repetitively;
wherein the axially spaced relationship between the electrode sets and the timing of the phase-locking of the electrical stimulus applied to the electrode sets are selected such that the local circumferential contractions are artificially propagated distally through the portion of the gastro-intestinal tract.
In a third aspect of the invention, the invention is directed at a method for electrical stimulation of smooth muscle comprising a portion of the gastro-intestinal tract, wherein the portion of the gastro-intestinal tract defines a longitudinal axis extending therethrough. The method is comprised of the steps of:
(a) applying an electrical stimulus at a proximal location to the smooth muscle circumferentially about the portion of the gastro-intestinal tract in a plane substantially perpendicular to the longitudinal axis, wherein the electrical stimulus is sufficient to stimulate the smooth muscle to produce a local circumferential contraction at the proximal location;
(b) applying an electrical stimulus at at least one distal location to the smooth muscle circumferentially about the portion of the gastro-intestinal tract in a plane substantially perpendicular to the longitudinal axis, wherein the distal location is in axially spaced relationship relative to the proximal location and wherein the electrical stimulus is sufficient to stimulate the smooth muscle to produce a local circumferential contraction at the distal location and wherein the applied electrical stimulus is varied between each of the proximal and distal locations; and
(c) phase-locking the electrical stimulus applied at the proximal and distal locations such that the electrical stimulus is applied at the proximal and distal locations successively and repetitively;
wherein the axially spaced relationship between the proximal and distal locations and the timing of the phase-locking of the electrical stimulus applied to the locations are selected such that the local circumferential contractions are artificially propagated distally through the portion of the gastro-intestinal tract.
In each aspect of the invention, the phase locking of the electrical stimulus is preferably comprised of the application of the variable electrical stimulus at each location or at each electrode set for an interval of time which overlaps the application of the electrical stimulus to the next successive location or electrode set. More particularly, the application of the electrical stimulus at each location or to each electrode set preferably ceases following the commencement of the application of the electrical stimulus at the next successive location or to the next successive electrode set. In other words, the application of the variable electrical stimulus at a prior location or electrode set laps over, covers, extends beyond or coincides, at least in part, with the application of the electrical stimulus to at least the next successive location or electrode set.
Preferably, the interval of time of the application of the electrical stimulus at each location or to each electrode set is selected such that each local circumferential contraction produced thereby overlaps the next successive local circumferential contraction. More particularly, each local circumferential contraction preferably ceases following the commencement of the next successive local circumferential contraction. In other words, the prior local circumferential contraction preferably laps over, covers, extends beyond or coincides, at least in part, with at least the next successive local circumferential contraction.
Thus, in the first aspect of the invention, the timing mechanism of the device preferably applies the electrical stimulus to each electrode set for an interval of time in overlapping succession such that the application of the electrical stimulus to each electrode set ceases following the commencement of the application of the electrical stimulus to the next successive electrode set. In the second aspect of the invention, the applying step of the method is preferably comprised of applying the electrical stimulus to each electrode set for an interval of time in overlapping succession such that the application of the electrical stimulus to each electrode set ceases following the commencement of the application of the electrical stimulus to the next successive electrode set. Finally, in the third aspect of the invention, the phase-locking step of the method is preferably comprised of applying the electrical stimulus at each location for an interval of time in overlapping succession such that the application of the electrical stimulus at each location ceases following the commencement of the application of the electrical stimulus at the next successive location.
In each aspect, the interval of time of application of the electrical stimulus to each electrode set or at each location is variable between successive electrode sets or successive locations respectively. For instance, in the third aspect of the invention, the interval of time of application of the electrical stimulus at each proximal and distal location is variable between successive locations. In other words, the interval of time for which the electrical stimulus is applied may vary between one or more locations or between one or more electrode sets. Thus, as a result, the period or length of each local circumferential contraction produced thereby may also vary.
However, although the interval of time may vary as described, the interval of time of application of the electrical stimulus preferably decreases with each successive electrical stimulus. Thus, the interval of time of application of the electrical stimulus to each electrode set preferably decreases with each successive electrode set. Similarly, the interval of time of application of the electrical stimulus at each location preferably decreases with each successive location. Accordingly, the period or length of each local circumferential contraction produced thereby may also decrease with each successive local circumferential contraction.
As indicated, the interval of time of the application of each electrical stimulus is selected such that the application of each electrical stimulus ceases following the commencement of the application of the next successive electrical stimulus. However, preferably, the application of each electrical stimulus ceases following the commencement of the application of all successive electrical stimulus.
Further, the interval of time of the application of each electrical stimulus may be selected such that each local circumferential contraction produced thereby ceases following the commencement of the next successive local circumferential contraction. In addition, the interval of time of the application of each electrical stimulus may be selected such that each local circumferential contraction produced thereby ceases following the commencement of all successive local circumferential contractions.
In the preferred embodiment of the first aspect of the invention, the timing mechanism of the device applies the electrical stimulus to each electrode set for an interval of time in overlapping succession such that the application of the electrical stimulus to each electrode set ceases following the commencement of the application of the electrical stimulus to all successive electrode sets.
In the preferred embodiment of the second aspect of the invention, the applying step of the method is comprised of applying the electrical stimulus to each electrode set for an interval of time in overlapping succession such that the application of the electrical stimulus to each electrode set ceases following the commencement of the application of the electrical stimulus to all successive electrode sets.
Finally, in the preferred embodiment of the third aspect of the invention, the phase-locking step of the method is comprised of applying the electrical stimulus at each location for an interval of time in overlapping succession such that the application of the electrical stimulus at each location ceases following the commencement of the application of the electrical stimulus at all successive locations.
Further, the application of the electrical stimulus to each electrode set or at each location may cease at any time following the commencement of the application of the electrical stimulus at all successive electrode sets or locations respectively. However, preferably, the application of the electrical stimulus to each electrode set or at each location ceases substantially concurrently. Thus, the application of the electrical stimulus to each proximal and distal electrode sets preferably ceases substantially concurrently or at about the same time. Similarly, the application of the electrical stimulus at each proximal and distal location preferably ceases substantially concurrently or at about the same time.
Each electrical stimulus may be applied at each location or to each electrode set for any interval of time sufficient to produce the desired local circumferential contraction. However, preferably, the interval of time of the application of the electrical stimulus to each proximal and distal electrode set is less than or equal to about 24 seconds. Similarly, the applying step of the method is comprised of applying the electrical stimulus to each successive electrode set for an interval of time of less than or equal to about 24 seconds. Finally, the phase-locking step of the method is comprised of applying the electrical stimulus at each successive location for an interval of time of less than or equal to about 24 seconds. In the preferred embodiment of the invention in any aspect, the interval of time of application of the electrical stimulus is between about 4 to 24 seconds.
Preferably, in all aspects of the invention, a period of stimulation is provided in which an electrical stimulus is successively applied at each location or to each electrode set, followed by a period of no stimulation, or a period of rest, before repeating the application of the electrical stimuli. During the period of stimulation, the desired local circumferential contractions are artificially propagated distally through the portion of the gastro-intestinal tract. The period of no stimulation is provided prior to repeating the period of stimulation and the repetition of the artificial propagation of the local circumferential contractions.
Thus, in the first aspect of the invention, the timing mechanism of the device applies the electrical stimulus to the proximal and distal electrode sets such that the electrical stimulus is applied to the proximal and distal electrode sets in succession for a period of stimulation, following which there is a period of no stimulation before the next application of the electrical stimulus to the proximal and distal electrode sets. In the second aspect of the invention, the applying step of the method performed using the device is comprised of applying the electrical stimulus to the proximal and distal electrode sets such that the electrical stimulus is applied to the proximal and distal electrode sets in succession for a period of stimulation, following which there is a period of no stimulation before the next application of the electrical stimulus to the proximal and distal electrode sets. Finally, in the third aspect of the invention, the phase-locking step of the method is comprised of applying the electrical stimulus at the proximal and distal locations such that the electrical stimulus is applied at the proximal and distal locations in succession for a period of stimulation, following which there is a period of no stimulation before the next application of the electrical stimulus at the proximal and distal locations.
In all aspects of the invention, the period of no stimulation may be of any period or length of time and may be of any period or length of time relative to the period of stimulation. Preferably, the period of no stimulation is substantially equal to the period of stimulation. Further, the period of stimulation and the equivalent period of no stimulation are both selected to provide a period or length of time sufficient to permit the electrical stimulus to produce the local circumferential contractions and to permit the artificial propagation of the contractions through the portion of the gastro-intestinal tract, preferably in a manner facilitating at least a partial emptying thereof.
In the first, second and third aspects of the invention, the portion of the gastro-intestinal tract may be comprised of the esophagus, the stomach, the small intestine, the large intestine, the anal sphincter and combinations thereof. However, in the preferred embodiment, the portion of the gastro-intestinal tract is comprised of the stomach. Further, in all aspects of the invention, the artificial propagation of local contractions through the gastro-intestinal tract, and in particular the stomach, is preferably sufficient to facilitate at least a partial emptying thereof.
The electrical stimulus may be applied at any location which permits the electrical stimulus to produce a local contraction at the desired portion of the gastro-intestinal tract. Thus, the electrode sets of the device may be affixed, applied or implanted at any such location. However, preferably, the electrical stimulus is applied at a location in communication with, or within, the layers comprising the wall of the gastro-intestinal tract. In the preferred embodiment, the electrical stimulus is applied subserosally. Thus, the electrode sets of the device are preferably implanted subserosally in the gastro-intestinal tract.
Further, in the third aspect of the invention, the electrical stimulus is preferably applied at at least two distal locations, and more preferably, at at least three distal locations. The number of distal locations will be determined by, amongst other factors, the size or dimensions, and in particular the length, of the portion of the gastro-intestinal tract to be stimulated and by the desired parameters and effectiveness of the artificially propagated local circumferential contractions. In the preferred embodiment, the electrical stimulus is applied at three to five distal locations.
Similarly, in the first and second aspects of the invention, the device is preferably comprised of at least two distal electrode sets, and more preferably, at least three distal electrode sets. The number of distal electrode sets will similarly be determined by, amongst other factors, the size or dimensions, and in particular the length, of the portion of the gastro-intestinal tract to be stimulated and by the desired parameters and effectiveness of the artificially propagated local circumferential contractions. In the preferred embodiment, the device is comprised of three to five distal electrode sets. Thus, the device preferably includes a total of four to six electrode sets.
In the preferred embodiment, the proximal location is located in about the mid-corpus of the stomach. The distal locations are located distally to the proximal location and in an axially spaced relationship with each other such that the phase-locking of the electrical stimulus produces a local circumferential contraction at the proximal location and each distal location in succession. Similarly, the proximal electrode set is located in about the mid-corpus of the stomach. The distal electrode sets are located distally to the proximal electrode set and in an axially spaced relationship with each other such that the phase-locked electrical stimulus produces a local circumferential contraction at the proximal electrode set and each distal electrode set in succession.
As well, in the first and second aspects of the invention, each of the proximal and distal electrode sets of the device is comprised of at least one active electrode and at least one ground electrode. Preferably, the active electrodes are connected to the power source, and the electrical stimulus is applied to the active electrodes, in a manner such that the electrical stimulus is provided concurrently to each of the active electrodes included in an electrode set.
In the preferred embodiment, each active electrode is paired with a ground electrode. However, the active electrodes may share one or more ground electrodes. For example, the electrode set may be comprised of a single ground electrode and one or more active electrodes. Thus, in the preferred embodiment, the number of active electrodes is greater than or equal to the number of ground electrodes in each of the proximal and distal electrode sets.
The electrodes of each electrode set may be spaced apart circumferentially about the portion of the gastro-intestinal tract at any distance permitting the electrical stimulus to produce a local circumferential contraction. However, in the preferred embodiment, the distance between the electrodes in each of the proximal and distal electrode sets is between about 2 to 4 centimeters. Thus, the specific number of electrodes comprising an electrode set will be dependent upon the specific circumference of the portion of the gastro-intestinal tract at the location of the electrode set.
Although the electrical stimulus applied at each of the proximal and distal locations, and to the proximal and distal electrodes, may be either direct or alternating, the electrical stimulus is preferably alternating. Thus, in the first aspect of the invention regarding the device, the electrical stimulus is preferably provided by an alternating voltage source. Further, although the electrical stimulus is variable and may be varied between each of the locations or electrode sets, all of the electrical stimuli are preferably alternating.
As well, although the alternating electrical stimulus may be either monopolar or bipolar, the alternating electrical stimulus is preferably bipolar. Thus, the alternating voltage source of the device is preferably a bipolar alternating voltage source. Again, although the electrical stimulus is variable and may be varied between each of the locations or electrode sets, all of the electrical stimuli are preferably bipolar.
Finally, each alternating electrical stimulus may have any shape suitable for producing the local circumferential contractions. However, the shape of each alternating electrical stimulus is preferably rectangular or square. Thus, the alternating voltage source is preferably a rectangular alternating voltage source or a square alternating voltage source. Further, although the shape of the alternating electrical stimulus is variable and may be varied between each of the locations or electrode sets, all of the alternating electrical stimuli are preferably rectangular or square.
Each alternating voltage source and each alternating electrical stimulus may have any frequency compatible with and capable of producing the desired local circumferential contraction without causing any significant damage to the tissues of the gastro-intestinal tract. However, the frequency of each alternating voltage source, in the first aspect of the invention, and the frequency of each alternating electrical stimulus, in the second and third aspects of the invention, is preferably between about 5 to 500 Hertz, and more preferably, is between about 5 to 50 Hertz, wherein the frequency is variable between each of the locations or electrode sets. In the preferred embodiment, the frequency is about 50 Hertz. Further, although the frequency of the alternating electrical stimulus or the alternating voltage source is variable and may be varied between each of the locations or electrode sets, the frequency of every alternating electrical stimuli or every alternating voltage source is preferably substantially the same, being about 50 Hertz in the preferred embodiment.
Each alternating voltage source and each alternating electrical stimulus may have any voltage compatible with and capable of producing the desired local circumferential contraction without causing any significant damage to the tissues of the gastrointestinal tract. However, the voltage of the alternating voltage source, in the first aspect of the invention, and the voltage of the alternating electrical stimulus, in the second and third aspects of the invention, is preferably less than or equal to about 20 Volts, peak to peak, and more preferably, is less than or equal to about 15 Volts, peak to peak, wherein the voltage is variable between each of the locations or electrode sets. In the preferred embodiment, the voltage is between about 4 to 14 Volts, peak to peak.
Further, as stated, the voltage of the alternating electrical stimulus or the alternating voltage source is variable and may be varied between each of the locations or electrode sets. Preferably, the voltage of the alternating electrical stimulus or the alternating voltage source decreases with each successive location or electrode set. Thus, in the second aspect of the invention, the applying step of the method is preferably comprised of varying the voltage of the alternating electrical stimulus between each of the proximal and distal electrode sets. More preferably, the applying step of the method is comprised of decreasing the voltage of the alternating electrical stimulus applied to each successive electrode set. In the third aspect of the invention, the voltage of the alternating electrical stimulus applied at the proximal location preferably varies from the voltage of the alternating electrical stimulus applied at each successive distal location. More preferably, a decreasing voltage is applied at each successive location.